If you use PHP suEXEC, it should assign dedicate PHP processes for each account, so it will take care of cpu/memory limits.

Right now, it is not possible to limit the total connections per vhost, the reason is that when server accept a new connection, it has no idea which vhost it is for before receiving the full request. If this vhost is IP based vhost with a dedicate IP, it is possible to implement a connection limit, but it is not available in LSWS yet.

Usually, connection is cheap, so it wont be a problem unless your server is under attack.